Synthesis of Au nanoparticle doped SiO2-TiO2 films:: tuning of Au surface plasmon band position through controlling the refractive index

The position of the surface plasmon resonance (SPR) band of Au nanoparticles was tailored by controlling the refractive indices (n) of the embedding matrices, to develop different coloured coatings on glass substrates. Five sets of Au nanoparticle doped coatings were prepared from sols derived from tetraethyl orthosilicate-3-(glycidoxypropyl) trimethoxysilane-titanium tetraethoxide containing gold chloride, following a sol-gel dip-coating method. The film samples of nominal formula (SiO2)(x)(TiO2)(0.97-x)Au-0.03(x = 0.97, 0.679, 0.485, 0.388 and 0.242) were prepared after heat treatment at 500 degrees C in air. The Au SPR peak, in the case of a SiO2 host ( SiO2 : TiO2 5 1 : 0, n = 1.411), observed at 542 nm, gradually red-shifted to 600 nm upon increasing the TiO2 content (SiO2 : TiO2 = 1 : 3, n = 1.939). As a consequence, a systematic change of the Au SPR position yielded pink, magenta, violet, royal and blue coloured coatings on ordinary sheet glasses. The formation of Au nanoparticles in the above gel and glassy coating matrices was monitored by UV-visible and FTIR spectroscopy, X-ray diffraction and transmission electron microscopy.